1. Technical Field
The invention relates generally to the manufacture of semiconductor devices. More particularly, the invention relates to a method for removing contaminants from a semiconductor wafer by applying a cleaning solution to the wafer as part of the spin coat fabrication process.
2. Background
Thin film fabrication techniques are commonly used in the manufacture of semiconductor devices. A variety of materials can be deposited as thin films, including photoresist, metals, and insulators. The composition and uniformity of thin films must be strictly controlled to facilitate etching submicron features into these films. Some of these materials are applied by coating the semiconductor wafer with a liquid which is dried to form a thin solid film. The liquid materials are most often coated onto the wafer using either a spin or spray coating process. In a conventional spin coating process, coating materials are applied by flowing liquid coating material onto the top surface of the semiconductor wafer while it is spinning. The wafer is held on a disk shaped, rotating spin chuck. The diameter of the chuck is typically somewhat less than the diameter of the wafer. The chuck is positioned so that the wafer lies on the chuck in a level horizontal plane. In operation, the bottom/inactive surface of the wafer is placed onto the chuck. The chuck applies a suction to the bottom of the wafer to hold the wafer in place on the chuck. The chuck is rotated by a motor driven axle that extends down from the chuck. As the wafer is rotated on the chuck, liquid coating material is applied to the center of the wafer. The coating material spreads radially outward from the center of the wafer towards the periphery to coat the top of the wafer. Ideally, all excess coating material is ejected from the periphery of the wafer. In practice, however, some excess material collects at the periphery of the wafer. The bead of coating material that forms at the periphery of the wafer is commonly referred to as an xe2x80x9cedge bead.xe2x80x9d In addition, coating material often splashes onto the exposed bottom surface of the wafer.
After the material has been spin coated onto the wafer, a solvent is dispensed along the periphery of the wafer and on the exposed bottom surface or xe2x80x9cbacksidexe2x80x9d of the wafer to dissolve the edge bead and remove the coating material from the periphery and bottom of the wafer. The edge bead removal solvent may dispensed through a nozzle directed toward the bottom of the wafer, in which case it curls up around to the top of the wafer to dissolve the edge bead, or the solvent may be dispensed directly onto the periphery of the wafer, or preferably both. The edge bead removal solvent may leave trace amounts of coating material residue on the periphery and exposed bottom surface of the wafer. Unwanted residue, particularly metal residue, on the periphery and bottom of the wafers is a source of potentially harmful cross-contamination. Photoresist and other common coatings are formulated to have low metallic ion on transition metal contamination. However, sufficiently low metallic ion contamination and other film performance criteria cannot always be achieved simultaneously. For example, newer film formulations intended for use in ferroelectric random access memory (FRAM) applications contain metals. These metallic film formulations, which are necessary for FRAM device performance, are a source of contamination that may be carried to other wafers, products and processing stations.
The present invention is directed to a novel method for removing contaminants from a semiconductor wafer having a spin on coating of material. Contaminants are removed by applying a cleaning solution to the periphery, and preferably, the exposed backside of the wafer after the edge bead has been dissolved and removed. The cleaning solution is formulated to react chemically with unwanted coating material residue to form a compound that may be ejectd from the periphery of the spinning wafer. Any residual solution or precipitate that is not ejected from the wafer may be rinsed away with water, preferably deoinized water. One exemplary use of this method is the removal of metallic contaminants that may be left on the periphery and backside of a wafer after the formation of ferroelectric film coatings. A cleaning solution comprising a mixture of hydrochloric acid HCL and water H2O or ammonium hydroxide NH4OH and water H2O is applied to the periphery of the spinning wafer. The cleaning solution will react with any residual metal ions to forma metal chloride or metal hydroxide that is ejected from the wafer along with the cleaning solution.